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In marine ecosystems top predator populations are shaped by environmental factors affecting their prey abundance. Coupling top predators’ population studies with independent records of prey abundance suggests that prey fluctuations affect fecundity parameters and abundance of their predators. However, prey may be abundant but inaccessible to their predators and a major challenge is to determine the relative importance of prey accessibility in shaping seabird populations. In addition, disentangling the effects of prey abundance and accessibility from the effects of prey removal by fisheries, while accounting for density dependence, remains challenging for marine top predators. Here, we investigate how climate, population density, and the accessibility and removal of prey (the Peruvian anchovy Engraulis ringens) by fisheries influence the population dynamics of the largest sedentary seabird community (≈ 4 million individuals belonging to guanay cormorant Phalacrocorax bougainvillii, Peruvian booby Sula variegata and Peruvian pelican Pelecanus thagus) of the northern Humboldt Current System over the past half‐century. Using Gompertz state–space models we found strong evidence for density dependence in abundance for the three seabird species. After accounting for density dependence, sea surface temperature, prey accessibility (defined by the depth of the upper limit of the subsurface oxygen minimum zone) and prey removal by fisheries were retained as the best predictors of annual population size across species. These factors affected seabird abundance the current year and with year lags, suggesting effects on several demographic parameters including breeding propensity and adult survival. These findings highlight the effects of prey accessibility and fishery removals on seabird populations in marine ecosystems. This will help refine management objectives of marine ecosystems in order to ensure sufficient biomass of forage fish to avoid constraining seabird population dynamics, while taking into account of the effects of environmental variability.

Abstract:The Peruvian anchovy fishery is the largest worldwide in terms of catches. The fishery started during the mid 1950s, and since then it has been highly dependent on natural stock fluctuations, due to the sensitivity of anchovy stocks to ocean-climate variability. The main driver of anchovy stock variability is the El Niño Southern Oscillation (ENSO), and three extreme ENSO warm events were recorded in

et al.. Ecosystem scenarios shape fishermen spatial behavior. The case of the Peruvian anchovy fishery in the Northern Humboldt Current system. Progress in Oceanography, Elsevier, 2014, 128 (11), pp.60 -73. Abstract 64 A major goal in marine ecology is the understanding of the interactions between the dynamics of 65 the different ecosystem components, from physics to top predators. While fishermen are among 66 the main top predators at sea, almost none of the existing studies on ecology from physics to top 67 predators contemplate fishermen as part of the system. The present work focuses on the coastal 68 processes in the Northern Humboldt Current System, which encompasses both an intense climatic 69 variability and the largest monospecific fishery of the world. From concomitant satellite, acoustic 70 survey and Vessel Monitoring System data (~90000 fishing trips) for a ten-year period (2000-2009), 71 we quantify the associations between the dynamics of the spatial behavior of fishermen, 72 environmental conditions and anchovy (Engraulis ringens) biomass and spatial distribution. Using 73 multivariate statistical analyses we show that environmental and anchovy conditions do 74 significantly shape fishermen spatial behavior and present evidences that environmental 75 fluctuations smoothed out along trophic levels. We propose a retrospective analysis of the study 76 period in the light of the ecosystem scenarios evidenced and we finally discuss the potential use of 77 fishermen spatial behavior as ecosystem indicator. 78 79 80 81 Highlights 82 Relationships between the environment, fish and fishermen were quantified in the Northern 83 Humboldt Current System. 84Ecosystem scenarios do shape fishing spatial behavior. 85Environmental fluctuations are smoothed out along trophic levels 86We propose ecosystem scenarios and fishermen response to each of them. 87 88 Keywords 89 Environmental conditions; fish distribution; coastal processes; anchoveta Engraulis ringens; 90 oxygen minimum zone; vessel monitoring system; fishers. 91 92 93

In the highly productive Northern Humboldt Current System, 3 seabird species, the Guanay cormorant Phalacrocorax bougainvillii, the Peruvian booby Sula variegata and the Peruvian pelican Pelecanus thagus, commence breeding in austral spring, coinciding with the lowest availability of their prey, the Peruvian anchovy Engraulis ringens. This strategy ensures the matching of increased prey availability when young achieve independence in summer. This pattern was observed during the last decade when anchovy was abundant. However, over the last century, the abundance of anchovy has varied widely due to contrasting interdecadal regimes in oceanographic conditions and fishing activity. We hypothesized that these regime shifts affected the abundance and availability of prey and may have conditioned the breeding seasonality of seabirds. We examined the timing and magnitude of the onset of breeding using dynamic occupancy models and related these parameters to the seasonality of oceanographic conditions, abundance of anchovy and fishing pressure. During a regime of lower anchovy abundance (1977−1990), cormorants showed the highest flexibility, adjusting the timing of breeding from spring to winter and skipping reproduction in the worst conditions. Boobies showed the lowest flexibility, maintaining the same magnitude and timing of onset of breeding in spring. Pelicans showed intermediate flexibility, foregoing breeding during the worst conditions, but maintaining the onset of breeding in spring. The 3 species used sea surface temperature as a cue for the initiation of breeding. Furthermore, given their better diving abilities, cormorants could monitor prey availability changes associated with the reversion in the seasonality of the oxycline depth. KEY WORDS: Onset of breeding • Environmental cues • Oxycline depth • NHCS • Northern Humboldt Current System • Phalacrocorax bougainvillii • Sula variegata • Pelecanus thagus Resale or republication not permitted without written consent of the publisher This authors' personal copy may not be publicly or systematically copied or distributed, or posted on the Open Web, except with written permission of the copyright holder(s). It may be distributed to interested individuals on request.